Transfer apparatus

ABSTRACT

Apparatus for preventing externally induced shock waves from being translated by a sheet of final support material into an image transfer region wherein toner images are being transferred from an intermediate surface, such as a photosensitive plate, onto the support material. Dampening rollers are positioned at the entrance and exit to the transfer region capable of contacting the support material so as to uniformly tension the material during the image transfer operation.

United States Patent Thettu July 8, 1975 [54] TRANSFER APPARATUS3,687,539 8/]972 Furuichi........ 355/3 X [75] Inventor: Raghulinga R.Thettu, Webster, FOREIGN PATENTS OR APPLICATIONS 1,522,653 ll/l969Germany 355/3 [73] Assignee: Xerox Corporation, Stamford,

Conn. Primary Examiner.lohn M. Horan [22] Filed: July 16, 1973 Appl.No.: 379,273

lllllllillllllm J" l 5 7 1 ABSTRACT Apparatus for preventing externallyinduced shock waves from being translated by a sheet of final supportmaterial into an image transfer region wherein toner images are beingtransferred from an intermediate surface, such as a photosensitiveplate, onto the support material. Dampening rollers are positioned atthe entrance and exit to the transfer region capable of contacting thesupport material so as to uniformly tension the material during theimage transfer operation.

1 Claim, 4 Drawing Figures 1 TRANSFER APPARATUS This invention relatesto apparatus for transferring a toner image from a photosensitive platesurface onto a sheet of final support material.

More specifically, this invention relates to a device for eliminatingskips and smears from being created upon a final copy made from anoriginal when pro duced, as for example, by the reusable xerographicprocess. It should be apparent, however, that the apparatus of thepresent invention is not necessarily limited to use in the reusablexerographic process and this invention has wider application in anymachine type environment wherein toner images are to be transferred froman intermediate support surface onto a final support sheet, such aspaper, Mylar, or the like in image configuration. The term skips andsmears, as herein used, relates to any deleterious effect on thefidelity of the created image resulting from the image being transferredfrom the intermediate support surface to the sheet of final supportmaterial.

In the automatic reusable xerographic art, a latent electrostatic imageof an original to be copied is conventionally recorded upon the surfaceof a moving photosensitive member, such as a selenium coated plate, andthe image rendered visible by applying charged toner particles to theplate surface. The visible toner image is then transferred from theplate onto a sheet of final support material that is brought into movingover lying contact therewith. Transfer of the image is generallyaccomplished by electrically attracting the toner particles from theplate surface onto the contacting side of the support sheet in imageconfiguration. The electrical force field for achieving the desiredtransfer operation can be created in many different ways, however,spraying the back side of the copy sheet with appropriately polarizedcorona is the most widely employed technique used in the art today.

It has been found, particularly when transferring images onto light bondpaper, that the image is oftentimes smeared or otherwise degraded duringthe transfer operation thereby reducing the quality of the copyproduced. Investigations of this smearing problem have shown that mostsmears are induced as a result of shock waves, that are generallypropagated outside of the transfer zone, being transmitted by thesupport material into the transfer regions. These shock waves cause thesupport sheet, while moving in contact with the photoreceptor, to bedisplaced or otherwise disturbed during the transfer operation. Theintegrity of the transfer operation is thus violated which results inblurred r smeared images being recorded upon the final copy.

It is therefore an object of the present invention to improve apparatusfor transferring xerographic toner images from a photosensitive plateonto a sheet of final support material.

It is a further object of the present invention to eliminate imagesmearing during a xerographic transfer operation.

A further object of the present invention is to prevent shock wavesinduced in the final support sheet from being transmitted into axerographic image transfer zone.

These and other objects of the present invention are attained by meansof an image transfer device wherein a sheet of final support material isbrought into moving contact with a moving toner image bearingphotosensitive plate surface, the transfer station including a transfercorona generator arranged to effect transfer of the toner images fromthe plate surface to the contacting surface of the support sheet anddampening means located at both sides of the image transfer region beingpositioned to contact the support sheet moving through the transferregion such that external induced disturbances translated to the supportmaterial are absorbed by said dampening means whereby the supportmaterial is brought through the transfer region in an undisturbedposture.

For a better understanding of the present invention as well as otherobjects and further features thereof. reference is had to the followingdetailed description of the invention to be read in connection with theaccompanying drawings, wherein:

FIG. 1 is a schematic drawing of an automatic xerographic copyingmachine embodying the teachings of the present invention;

FIG. 2 is an enlarged view of the image transfer station of theautomatic xerographic copying machine illustrated in FIG. 1 showingshock dampening means being strategically located therein to isolate thesupport material as it moves through the transfer region;

FIG. 3 is an enlarged perspective view of a typical dampening meansemployed in the preferred embodiment of the present invention; and

FIG. 4 is a cross-sectional view of the dampening means illustrated inFIG. 3.

Referring now to FIG. I, there is illustrated a schematic representationof an automatic xerographic reproducing machine employing an imagetransfer mechanism embodying the teachings of the present invention. Itshould be noted that the apparatus of the present invention will beexplained in conjunction with the reusable xerographic copying process.However, it should be clear to one skilled in the art that the apparatusof the present invention is not so limited in its usage and that theinvention has wide application in any copying environment in which animage is to be transferred from an intermediate surface onto a sheet offinal support material.

Because the xerographic copying process is well known and used in theart, the processing steps herein involved will be only briefly describedwith reference to FIG. I. A photosensitive plate 10, in drumconfiguration, is mounted upon a horizontally aligned shaft 12 andcaused to rotate in the direction indicated so that the drum surfacepasses sequentially through a series of processing stations. Thexerographic plate basically consists of an outer layer 13 ofphotoconductive material, such as selenium or the like, that is placedover a grounded substrate 14.

In operation, the plate is initially charged to a uniform potential at acharging station A by means of corona generator 15. The uniformlycharged plate is then moved into an imaging station E wherein a flowinglight image of an original document, which is supported upon transparentviewing platen 17, is projected onto the photoconductive plate surfaceby means of a moving scanning lens element 18 and a pair of mirrors l9and 20. As a result of the imaging process, a latent electrostatic imagecontaining the original subject matter is recorded upon thephotoconductive plate. The latent image is next transported on the drumsurface through a developing station C wherein the latent image isrendered visible by the application of an especially pre pared chargedtoner material by cascading the material over the image plate surface.

The visible or toner developed image is then transported on the movingdrum surface into an image transfer station D embodying the teachings ofthe present invention. As will be explained in greater detail below, asheet of final support material is fed from either one of two supplytray areas, an upper supply tray area 24 and a lower supply tray area25, via a sheet registering and forwarding mechanism 30, into thetransfer station in moving synchronous contact with the visible imagecarried on the drum surface. The support sheet and the charged tonerimage on the drum surface move to gether under a corona charging device27 which serves to electrostatically transfer the toner images from theplate surface to the contacting side of the support sheet. The sheet isthen stripped from the drum surface by means of a picker finger 28 anddirected along a stationary vacuum transport 29 into the nip ofa heatpressure roll fusing assembly F. For further details concerning thistype of fusing device, reference is herein had to U.S. Pat. No.3,498,596 which issued in the name of Moser.

As noted above, the automatic copier herein described has the capabilityof producing either single sided copy, that is, copy bearing a tonerimage on one side thereof, or double sided copy. in the single sidedmode of operation, the final support sheets are fed from either theupper supply tray or the lower supply tray directly into the imagetransfer station D. Upon the accomplishment of the transfer step, theimage sheet is then passed through the fuser roll assembly and forwardeddirectly into a collecting tray 21 where the copies are stored and helduntil such time as the operator removes them. On the other hand, when atwo sided copy mode of operation is selected, a movable transport 26 inthe paper path, is lowered to the dotted line position as shown in FIG.1 and the upper supply tray, which has been previously emptied of allsupport mate rials, is automatically prepared to accept the copy sheetdirected therein. The copy sheets are fed from the lower support traythrough the image transfer station and the image fusing station, and aredelivered into the upper support tray area where the once imaged copysheets are stored until the machine is further programmed for a secondcopy run. Upon the initialization of the second copy run, the movabletransport 26 is once again raised to the solid line position shown inFIG. 1 and the once imaged copy sheets are fed once again directly fromthe upper supply tray through the transfer and fusing stations wherein asecond image is created on the opposite non-imaged side of the sheet.After fusing, the two sided copy sheet is then fed directly into thecopy tray in the manner herein described.

Referring now more specifically to FIG. 2, there is shown in greaterdetail the image transfer station of the automatic copying machineherein described. At the beginning of each sheet feeding cycle,individual sheets of final support material are fed from either theupper supply tray or the lower supply tray into a sheet registration andforwarding mechanism 30 which is described in greater detail in US. Pat.No. 3,601,392. Herein, the leading edge of the individual sheets ofmaterial are registered with the visible toner image created on themoving drum surface and are then engaged by a pair of advancing rollers32, 33 which serve to forward the sheet at drum speed into the transferstation D. A pair of guide elements 35, 36 are provided to insure thatthe sheet contacts the drum surface prior to entering the corona streamemitted from transfer corona generator 27 and which herein defines theboundaries of the transfer region.

The sheet in process and the toner image contained on the drum surfacemove together through the corona stream wherein the toner image istransferred from the plate to the support sheet. lnvariably, during theelectrical transfer operation, the copy sheet becomes electricallytacked to the moving photoconductive surface. A pick off finger 28 ispositioned downstream from the transfer region with the tip of thefinger arranged to move between the support sheet and the plate surfaceand thus strip the sheet from the drum. The finger is further adapted todirect the sheet of material upwardly into communication with a vacuumplaten 37 associated with the stationary transport 29. Once in contactwith the platen, the sheet is guided along the platen surface into thenip of fuser assembly F wherein the image is affixed to the supportmaterial in the manner described in the previously noted Moser patent.

As can be seen, as the support sheet is moved through the transferstation, many different sheet han dling instrumentalities come into playthat act upon the sheet either alone or in concert, depending upon theposition of the sheet at any given point in time. For example, as shownin FIG. 2, in the extreme case, the support sheet is simultaneouslyhandled or acted upon by the cooperating advancing rolls 32, 33, thesheet pick off finger 28, the stationary vacuum transport 29 and thefuser rolls 40, 41 in fuser assembly F. Any obstacles or otherimpediment to the sheets motion during this period is imparted to thesupport material and is ultimately reflected as a shock wave which istransmitted along the length of the support material. This shock wave,as it moves through the transfer region, produces a movement of thesheet in the transfer region which results in a smeared or blurred imagebeing recorded on the final copy.

A set of dampening transport rollers, generally referenced 45, arestrategically positioned along the path of travel of the supportmaterial as it is being advanced through the transfer station betweenthe advancing rolls and the fuser assembly. As seen in FIGS. 3 and 4,the rollers consist of a stationary vacuum cylinder 46 and a rotatablesleeve 47 which is mounted thereupon so that the sleeve is capable offreely rotating about the peripheral surface of the cylinder. Thecylinder is provided with an elongated longitudinally extending vacuumport 48. In each end of the cylinder there is provided a hollow tube 49through which a vacuum is drawn by any suitable vacuum drawing means(not shown) whereby a relatively uniform negative pressure is createdalong the length of the port 48.

A pulley means 50 is affixed to the outboard end of the sleeve with thepulley being operatively connected to the main drive system of themachine. The pulley is arranged to rotate the sleeve so that thevelocity of the outer periphery of the sleeve is equal to the velocityat which the support material is advanced through the transfer station.The sleeve is provided with a series of obliquely offset apertures 52which are adapted to move in and out of fluid flow communication withthe elongated suction port 48 as the apertures are moved thereover so asto exert a uniform holding pressure upon the material within thetransfer region.

In practice, the dampening transports are mounted along the sheets pathof travel so that the sheet comes into contact with the dampeners sleevedirectly over the suction port 48. The rollers thus exert a holdingpressure upon the sheets as they move through the transfer station andthus serve to absorb any shock waves induced in the support material asit is moving through the region immediately below the transfer generator27.

Although three dampening rollers are utilized in the preferredembodiment of the present invention, it should be clear that in mostcases only two rollers, positioned at the exits and entrance zones tothe transfer region, are generally required in order to successfullyisolate induced shock waves from entering this critical area. As seen inFIG. 2, a dampening roller 45 (a) is positioned at the entrance to thetransfer region between the advancing rollers 32, 33 and the point wherethe copy sheet contacts the moving drum surface. Any shock wavesinitiated within the sheet registering and forwarding mechanisms 30 arethus absorbed by the roller prior to the waves entering the transferregion. Similarly, a second dampening roller 45 (b) is positioned at theexit to the transfer region and serves to absorb downstream inducedshocks as for example those created by the stripper finger acting uponthe copy sheet or the copy sheet being buckled or otherwise disturbed asit is moving along the stationary vacuum transport. It should be notedthat the exit dampening roll 45 (b) is positioned so that itcommunicates with the back side, or non-image side of the copy sheetthus preventing the roller from degrading the unfused toner imagesthereon. The two rollers, that is, the entrance dampening roller 45 (a)and the exit dampening roller 45 (b), coact to apply a holding forceupon the sheet thus producing a uniform tension over the entire lengthof the material as it moves through the transfer region. A thirddampening roller 45 (c) is also herein provided which is positionedbetween the stationary vacuum transport and the fuser nip to furtherprevent shock waves provocated in the fuser assembly from beingtransmitted back along the sheet into the transfer region.

Although a vacuum drawing transport roller is herein described, itshould be clear that any type of dampening means that is capable ofpreventing shock waves from entering a xerographic transfer region isconsidered within the scope of the present invention. For example, thedampening rollers can take the form of a solid cylindrical bar orcylinders of low durometer rubber with the rollers being positioned touniformly tension the support material as the transfer step is beingaccomplished.

While this invention has been described with reference to the specificstructure herein disclosed, it is not confined to the details as setforth, and this application is intended to cover any modifications orchanges as may come within the scope of the following claims.

What is claimed is:

1. Apparatus for transferring a charged toner image from the surface ofan image bearing plate onto a sheet of final support material includingmeans defining an image transfer zone for transferring the toner imagefrom the image bearing plate to the sheet of final support materialbrought in contact therewith within the transfer zone,

means for moving the sheet of final support material into and throughthe image transfer zone wherein at least a portion of the sheet moves incontact with the image bearing plate, and

dampening means positioned at the support material entrance and exitregions to the transfer zone for preventing shock waves which may beinduced in the support material outside of the transfer zone by themoving means from moving into the transfer zone, the dampening meansincluding at least one roller positioned at each of the regions andmounted to rotate so that the velocity of the outer periphery of eachroller is at least substantially equal to the velocity at which thesupport material is advanced through the transfer zone, and vacuumdrawing means associated with each roller for placing a uniform tensionupon the support material as it moves through the transfer zone, andwherein the roller positioned at the exit to the transfer zone isarranged to contact the non-image bearing side of the support material.

1. Apparatus for transferring a charged toner image from the surface ofan image bearing plate onto a sheet of final support material includingmeans defining an image transfer zone for transferring the toner imagefrom the image bearing plate to the sheet of final support materialbrought in contact therewith within the transfer zone, means for movingthe sheet of final support material into and through the image transferzone wherein at least a portion of the sheet moves in contact with theimage bearing plate, and dampening means positioned at the supportmaterial entrance and exit regions to the transfer zone for preventingshock waves which may be induced in the support material outside of thetransfer zone by the moving means from moving into the transfer zone,the dampening means including at least one roller positioned at each ofthe regions and mounted to rotate so that the velocity of the outerperiphery of each roller is at least substantially equal to the velocityat which the support material is advanced through the transfer zone, andvacuum drawing means associated with each roller for placing a uniformtension upon the support material as it moves through the transfer zone,and wherein the roller positioned at the exit to the transfer zone isarranged to contact the non-image bearing side of the support material.